# The Clausius Inequality

1. Oct 13, 2014

### Cassiano

Not sure if this was the right place for this but here goes.
Hello all, so I'm trying to get an intuitive grasp of the Clausius Clapeyron relation dP/dT= L/TdelV. Where L is the latent heat of the phase transition. What I've got so far is this; the relation tells you how much extra pressure must be exerted on a system in order to change its phase for every degree it is away from the temperature it changes phase at 1 atm. Is this correct?

Also the Tempertaure used in the equation would be the temperature of the phase change at standard conditions right? Thank you for the help

2. Oct 14, 2014

### Staff: Mentor

Hi Cassiano, welcome to PF!

Not exactly. It is the slope of the boundary between two phases in a PT-diagram. It is not related to any "standard" condition, be it 1 atm or something else. The temperature is simply the temperature at which you are considering the slope. Note also that it is $dP/dT$, not $\Delta P / \Delta T$, which is kind of implied by the way you formulated it. In other words, the relationship is not linear between the pressure and the temperature at which the transition takes place.